A motorcycle battery has a hard life: heat, vibration, short trips and long periods of standing. Maintenance is simple, but it must be done before the battery fails, not after. The owner's manual specifies whether the battery is serviceable or sealed.
At a glance
| Check | Healthy sign | Action if not |
|---|---|---|
| Resting voltage | About 12.6 V or above | Charge slowly and retest |
| Terminals | Clean and tight | Clean and apply dielectric grease |
| Charging voltage | Within the manual range at fast idle | Test stator and regulator |
| Case | Dry and undistorted | Replace a swollen or leaking battery |
| Storage | Charged and cool | Use a maintainer or monthly charge |
Know the battery type
A conventional lead-acid battery may have removable caps and an electrolyte level to check. An AGM or gel battery is sealed and should never be opened. A lithium battery has different charging requirements and must not be charged with a lead-acid charger unless it is compatible.
Use the correct charger for the type. A charger that is too powerful can overheat a small battery. A maintainer is useful for a bike that sits for weeks, but it must be voltage-regulated and suitable for the battery chemistry.
Tools and precautions
You need a multimeter, a battery charger or maintainer, a terminal brush, dielectric grease and eye protection. Work in a ventilated area away from sparks and flames. Batteries produce hydrogen, which is explosive.
Remove the negative terminal first and refit it last. This reduces the risk of a short circuit through a tool. Do not lean over a battery while charging. If electrolyte contacts your skin or eyes, flush with water and seek medical help.
Check voltage and terminals
Measure the resting voltage with the key off. A healthy 12 V battery should read around 12.6 V when fully charged. A reading near 12.0 V is partially discharged; lower than that suggests a deep discharge or a failing battery.
Inspect the terminals for white or green corrosion. Clean them with a brush and a suitable solution, then apply a thin film of dielectric grease. Check the ground strap and the battery hold-down. A loose battery can crack internally.
Charging and storage
Charge a discharged battery slowly with the correct charger. A fast charge can heat the battery and reduce its life. If the battery does not accept a charge or gets hot, replace it.
For storage, charge the battery fully, disconnect the negative terminal or use a maintainer, and keep it in a cool, dry place. A battery that is left flat for weeks will sulphate and lose capacity. Check the voltage monthly.
When to replace
Replace the battery if it will not hold a charge, the voltage collapses under load, the case is swollen or leaking, or it is more than a few years old and has become unreliable. A load test is more conclusive than a voltage reading.
Do not replace a battery without checking the charging system. A failed regulator can destroy a new battery in a short time. Measure the charging voltage at fast idle after fitting the new battery.
When to book the workshop
Book a workshop if the battery boils, smells of sulphur, leaks, or the charging voltage is outside the specification. A faulty charging system can damage the battery and the electronics.
If the bike has a parasitic drain, a workshop can measure the key-off current and isolate the circuit. Replacing the battery will not fix a drain.
The bottom line
A battery needs clean terminals, the correct charge and a healthy charging system. Check the voltage monthly, use a maintainer for storage and replace a battery that will not hold a charge. If it keeps failing, find the drain or the charging fault.IndoBikes workshop
Checklist
- Identify the battery type and charger requirement.
- Measure resting voltage with the key off.
- Inspect and clean the terminals.
- Apply dielectric grease to the terminals.
- Check the hold-down and ground strap.
- Charge slowly with the correct charger.
- Use a maintainer for long storage.
- Check the charging voltage after fitting.
- Replace a battery that will not hold a charge.
Questions
How often should I check the battery?
Check the voltage monthly and before a long trip. A bike that sits for weeks needs a maintainer or a monthly charge.
Can I charge a motorcycle battery with a car charger?
Only if the charger is suitable and the current is low enough. A fast car charger can overheat a small motorcycle battery. Use a motorcycle-specific charger or maintainer.
Why does my battery keep going flat?
A parasitic drain, a failing charging system, an old battery or short trips can all cause it. Test the charging voltage and the key-off current before replacing the battery.
